Organic electroluminescent devices are typically structured to include an organic electroluminescent element laminated on a substrate. The organic electroluminescent element includes at least a first conductive layer, an organic electroluminescent layer, and a second conductive layer. There have been studies to use such organic electroluminescent devices in applications such as in lighting devices. In the following, “organic electroluminescent” will be referred to simply as “organic EL.”
On the other hand, it is known that organic environmental pollutants (organic contaminants) in air and water are decomposable with a photocatalyst. A photocatalyst is a substance that shows catalytic effects upon being irradiated with light of a specific wavelength range. Specifically, a photocatalyst generates conductive electrons and holes in response to excitation (photoexcitation) of electrons in the valence band upon being irradiated with light of a specific wavelength range (excitation light having a higher energy than the band gap between the valence band and the conduction band of the photocatalyst). The photocatalyst can thus function as a catalyst that accelerates a variety of chemical reactions with the reducing power of the electrons generated in the conduction band, and the oxidizing power of the holes generated in the valance band as a result of photoexcitation.
Once activated and brought to the state that can exhibit the catalytic function in response to irradiation of excitation light, a photocatalyst can use its strong oxidizing power to decompose organic contaminants contained in air and water that are in contact with the photocatalyst.
There have been attempts to combine an organic EL element and a photocatalyst, and decompose organic contaminants in air for deodorization and sterilization purposes. Specifically, it is known to laminate a photocatalyst-containing photocatalyst layer on an organic EL element, activate the photocatalyst layer with the excitation light produced by emission of the organic EL element, and decompose organic contaminants through redox reaction (for example, PTL 1).
However, a photocatalyst layer typically has poor translucency. A problem of laminating a photocatalyst-containing photocatalyst layer on an organic EL element, then, is that the light from the organic EL element cannot easily pass through the photocatalyst layer, making it difficult to use the organic EL device with the photocatalyst layer for illumination applications.
One possible solution is to make the photocatalyst layer more translucent by reducing the thickness of the photocatalyst layer. A problem, however, is that reducing the thickness of the photocatalyst layer lowers the oxidizing and reducing power of the photocatalyst layer, and the photocatalyst fails to sufficiently decompose organic contaminants in air.
An ultraviolet responsive photocatalyst is a well known example of photocatalysts. Because of its large band gap, an ultraviolet responsive photocatalyst hardly shows activity unless irradiated with high energy ultraviolet light of short wavelengths (wavelengths of less than 380 nm). An organic EL element using an ultraviolet responsive photocatalyst as the photocatalyst in its photocatalyst layer thus requires emitting primarily ultraviolet light. However, ultraviolet light is not visible, and is harmful to human body and food. It is accordingly difficult to use an organic EL device with such a photocatalyst layer for lighting applications in rooms or refrigerators.
One way to overcome this problem is to form a photocatalyst layer with a photocatalyst (visible-light responsive photocatalyst) that can be activated with visible light (wavelengths of 380 nm to 780 nm) having smaller energy. However, the photocatalytic activity of a visible-light responsive photocatalyst is typically low (the oxidizing and reducing power is weak). A problem thus still remains that use of a conventional visible-light responsive photocatalyst for a photocatalyst layer is not sufficient to decompose organic contaminants.